Surface roughness is an important item to evaluate the surface quality. Many researches focused on the optimization of cutting parameters in the specified cooling/lubrication conditions. But the effect of different cooling/lubrication conditions was still less considered. Aimed at this problem, the effect of cutting parameters on the average surface roughness (Ra) in the different cooling/lubrication conditions, including MQL, wet, dry cutting, was analyzed in this study. Orthogonal arrays were applied in the design of the experiments and Ti6Al4V end-milling experiments were performed on the DAEWOO machining center. The white light interferometer was used to obtain the 3D profile of machined surface and calculate the Ra values. The regression analysis and statistical analysis of variance were employed in the process of the experimental data. The relationships between Ra and cutting parameters in the different cooling/lubrication conditions were obtained and the optimum values of the cutting parameters in the range of the experiments were selected.